Why are Japanese anti-cannabis laws so strict?

Here are some explanations from a very interesting Japan Times article on the history of cannabis in Japan:

‘Following the country’s defeat in 1945… the U.S. authorities occupying Japan brought with them American attitudes toward cannabis. Washington had effectively outlawed cannabis in the United States in 1937 and now it moved to ban it in Japan. In July 1948, with the nation still under U.S. occupation, it passed the Cannabis Control Act — the law that remains the basis of anti-cannabis policy in Japan today.

There are a number of different theories as to why the U.S. outlawed cannabis in Japan. Some believe it was based upon a genuine desire to protect Japanese people from the evils of narcotics, while others point out that the U.S. allowed the sale of over-the-counter amphetamines to continue until 1951. Several cannabis experts argue that the ban was instigated by U.S. petrochemical interests in a bid to shut down the Japanese cannabis fiber industry, opening the market to man-made materials such as polyester and nylon.

Takayasu locates the cannabis ban within the wider context of U.S. attempts to reduce the power of the Japanese military.

“In the same way that U.S. authorities discouraged kendo and judo, the 1948 Cannabis Control Act was a way to undermine militarism in Japan,” he says. “The wartime cannabis industry had been so dominated by the military that the Cannabis Control Act was designed to strip away its power.”’